This invention relates to improved transparent and flame-retardant compositions and more specifically to transparent, flame-retardant ABS resins.
Acrylonitrile-butadiene-styrene (ABS) resins have achieved wide-spread use in the plastics field in a variety of applications for the molding of plastic articles having good impact resistance. One of the early improvements in the formulation of ABS plastics was to blend ABS resins with polyhalogenated aromatic compounds such as polybrominated diphenyl oxides to impart flame retardancy to the composition. Such compounds have frequently been used with an inorganic synergist such as antimony oxide as described in U.S. Pat. Nos. 3,347,822, 4,144,288 and 4,173,561 as well as German Pat. Nos. 2,733,695, 2,933,900 and 3,142,894.
ABS resins may generally be characterized as a dispersion of a particulate rubbery impact modifier in a rigid polymeric matrix. As such, ABS resins are normally opaque materials, and the addition of inorganic flame retarding agents and synergists would be expected to contribute toward the opaqueness. There are, however, various applications where the lack of transparency in ABS resins prevents its use. Transparency in ABS systems has heretofore been accomplished by matching the refractive index of the grafted resin component to the impact-modifying rubber substrate, either by incorporating monomers such as methylmethacrylate or methacrylonitrile in the grafted component, or by employing modified rubbery substrates such as acrylate rubber as the impact modifier. Such modifications are known to affect other physical properties including solvent resistance, and the cost and complexity of the resin is increased. A method for improving the transparency of ABS resins without requiring modification of the base resin would be a useful improvement in the compounding art.